The collision detection has some inaccuracy/error around the edges of Rectangular fixture.Please see picture, yellow box is controlled by player and it is moving toward blue spheres.As blue spheres slide toward the edge of the box, the error (penetration) increases.

There must be something else going on. It would be really helpful if you could put together a junit-test or a simple app with full source code to duplicate your problem.

I gave up. This library is really hard to use. I did try using same configuration values from Shapes.xml in the sandbox.Changed all spheres to Rectangular fixtures, problem still exists.Code is all single threaded, no fancy stuffs.The spheres are still overlapping the box, the wider the box the worse the problem becomes.

I understand you may be frustrated, but it's difficult for us to offer help without more information. Zoom is correct, we need some way to replicate and the best way to do so would be through a code sample.

If you are new to the library I would recommend you start there. If you can get one of those working - as is - then modify one thing at a time to get to where you want to be. It's quite possible that you've just missed something trivial, yet critical.

The issue dissapears if I set MassType of the non-player bodies to INFINITY. Thus i am restricted with non-moving rectangular object.Not sure if this issue only occurs with Rectangle, haven't tried creating Convex object using triangles.